Definition
A laboratory cupping tester, also known as a cupping tester or Erickson tester, is a specialized material testing instrument used to evaluate the ductility and rupture resistance of sheet metal or strip during stamping. Its core function is to simulate the forming behavior of the material under bidirectional tensile stress, and quantify the forming performance of the material by measuring the maximum depth that the specimen can withstand before it breaks, i.e. the cupping value. This test is widely used in quality control and R&D in materials science, metalworking and manufacturing.
Principle
The basic principle of cupping test is based on the expansion process of the plate. During the test, the specimen is firmly clamped between the crimping ring and the die, and a spherical punch of the specified size is used to apply pressure to the specimen at a uniform speed. The specimen is plastically deformed into the die under the action of the punch, and gradually forms a bulge until it ruptures. The limit depth of punch movement, i.e. the displacement value at the moment of specimen rupture, is recorded as cupping depth. This depth value directly reflects the ability of the material to resist local thinning and cracking under complex stress conditions, and its theoretical basis is closely related to the tensile instability criterion in metal plastic forming.
Measurement method
The standard cupping test follows a strict procedure. First, a square or round specimen of the specified size is prepared according to relevant standards (e.g., ISO 20482, GB/T 4156). The specimen is placed between the die and the rim ring, and the edge of the specimen is sufficiently pressed through the specified edge pressure to prevent material inflow. Subsequently, the device is activated and the ball punch stamps the center of the specimen at a constant speed. During the test, the equipment continuously monitors the punch displacement and load. When the specimen has a penetrating crack, the test will be stopped automatically, and the displacement displacement of the punch will be the cupping depth. Some advanced instruments integrate optical or electrical sensors to accurately determine the rupture point.
Influencing factors
Cupping test results are influenced by multiple factors, and understanding these factors is crucial to ensure data accuracy and comparability. The intrinsic properties of the material are the decisive factors, including the material's chemical composition, microstructure, anisotropy, work hardening index, and thick isotropy coefficient. Test conditions are also critical, such as the geometry of the punch and die, surface roughness, the amount of edge pressing force, the test speed and the lubrication conditions. Specimen preparation normatives, such as edge burrs and surface scratches, can also introduce biases. Therefore, strict adherence to the test parameters specified by the standard is a prerequisite for reliable and reproducible results.
Application:
Cupping instruments have a wide range of application value in the fields of industry and scientific research. In the field of sheet metal production, such as steel and non-ferrous metal processing enterprises, it is used for incoming material inspection, production process monitoring, and quality assessment of the final product. In industries such as automotive, aerospace, and home appliances where stamping is the primary manufacturing process, cupping tests are used to screen plates, evaluate the feasibility of mold design options, and optimize stamping process parameters. In the field of research and development, it serves the development of new materials, helping researchers evaluate the effect of different alloy compositions or heat treatment processes on the formability of materials.
Selection
Choosing a suitable laboratory cup protrusion instrument requires comprehensive consideration of technical parameters and application requirements. The core parameters include the test force range, displacement measurement accuracy, maximum cupping depth and edge pressure control mode. The equipment should be compatible with the mold size specified by mainstream international and domestic standards. Automation is another consideration, with manual, semi-automatic, and fully automated models offering operational efficiency, consistency of results, and labor costs. In addition, it is necessary to evaluate whether the device's data acquisition and analysis software capabilities support direct data export, curve drawing, and report generation. The rigidity and long-term stability of the equipment, as well as the manufacturer's technical support and calibration services, are also important aspects of long-term reliable operation.